The enormous importance of peptidal hormone and neurotransmitter agonists and antagonists and of peptidal inhibitors of proteolytic enzymes is well understood. However, peptides are rapidly degraded in vivo by exo and endo peptidases. Another shortcoming of peptides as potential therapeutic agents is their lack of bioavailability by the oral route. The latter deficiency appears to be due in part to the amide backbone. We propose to synthesize novel mimics of peptide hormone agonists/antagonists which are devoid of the amide backbone. The peptide side chains are to be retained in the appropriate spatial disposition. In the case of the enzyme inhibitor mimics, provision is also made for H-bonding interactions with the enzyme backbone. Such H-bonding is not required for the interaction of hormone agonists/antagonists with their receptors. The proposed synthetic targets are designed to serve as mimics or antagonists of somatostatin, substance P, the chemotaxis-related formyl tripeptide, and the fibrinogen receptors. The proposal is also concerned with inhibitors of the proteolytic enzyme renin and other aspartate proteases, notably the HIV1 protease of importance in AIDS.